\Header{SSgompertz}{Gompertz Growth Model}
\keyword{models}{SSgompertz}
\begin{Description}\relax
This \code{selfStart} model evaluates the Gompertz growth model
and its gradient.  It has an \code{initial} attribute that
creates initial estimates of the parameters \code{Asym},
\code{b2}, and \code{b3}.\end{Description}
\begin{Usage}
\begin{verbatim}
SSgompertz(x, Asym, b2, b3)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a numeric vector of values at which to evaluate the model.
\item[\code{Asym}] a numeric parameter representing the asymptote.
\item[\code{b2}] a numeric parameter related to the value of the function at
\code{x = 0}
\item[\code{b3}] a numeric parameter related to the scale the \code{x} axis.
\end{ldescription}
\end{Arguments}
\begin{Value}
a numeric vector of the same length as \code{input}.  It is the value of
the expression \code{Asym*exp(-b2*b3\textasciicircum{}x)}.  If all of
the arguments \code{Asym}, \code{b2}, and \code{b3} are
names of objects the gradient matrix with respect to these names is attached as
an attribute named \code{gradient}.\end{Value}
\begin{Author}\relax
Douglas Bates\end{Author}
\begin{SeeAlso}\relax
\code{\Link{nls}}, \code{\Link{selfStart}}\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
data(DNase )
DNase.1 <- subset(DNase, Run == 1)
SSlogis(log(DNase.1$conc), 4.5, 2.3, 0.7)  # response only
Asym <- 4.5; b2 <- 2.3; b3 <- 0.7
SSgompertz(log(DNase.1$conc), Asym, b2, b3 ) # response and gradient
getInitial(density ~ SSgompertz(log(conc), Asym, b2, b3),
           data = DNase.1)
## Initial values are in fact the converged values
fm1 <- nls(density ~ SSgompertz(log(conc), Asym, b2, b3),
           data = DNase.1)
summary(fm1)
\end{ExampleCode}
\end{Examples}

